RBRE960B compatibility with BGW320-500

Hi, 

I'm currently running an AT&T Fiber connection with a BGW320-500 modem/router combo unit. First week of March I picked up an Orbi RBRE960B and swapped out my old Netgear Nighthawk for it. I immediately (quite literally the first time I powered everything back up) started having issues with my Modem seeming to be unable to sync to the AT&T Network. (AT&T has been quite confused by the situation because the modem flashes white when trying to come back up, not red which would indicate a network issue. They also tried 5 different modems, all with the same result). I'm somewhat fluent in networking and understood exactly how "my router is preventing my modem from syncing" sounds, which is why it's now two months later and I haven't done too much reaching out, but I'm at my wits end here with this now and coming up on more drastic solutions like changing ISP.

Over the last two months I've done a fair bit of troubleshooting. Removed satellites thinking they were too close together (and I'm sure they were). The last week I haven't been using any of the satellites, just the router alone. What I've been seeing, which has remained consistent the entire time, is that when the modem drops, if I disconnect the Orbi from the power source, the modem comes back online within minutes. I've confirmed this pattern easily more than two dozen times, and it always works. My internet has been down nearly all week (AT&T said they saw 114 disconnects in one day) so I finally swapped my Nighthawk back into the mix a few days ago. This has resolved the issue entirely.

Has anyone seen or heard of this kind of issue before? I'd like to get a replacement for my router and verify if it's truly a compatibility issue or some kind of defect with my router. I'm relatively sure it's not a configuration problem at this point, but maybe I'm missing something there. But I was fairly certain Netgear would likely just say "you can't use two router devices in the same home" and so far my brief conversation with Netgear seems to confirm those expectations, as that's exactly what I got from the call I just had with Netgear support. "Don't use a modem/router combo, I'll escalate your case".

Any thoughts on this? I actually have a self install kit in the mail from another internet provider. One where I could use my own modem. But after confirming with the Nighthawk that everything works just fine with a different router connected, I'm kind of wanting to cancel that and stick with AT&T. Their service has been flawless for two years. Something I couldn't say about the competitor in the past, which is why I switched in the first place. But I'd really like to find a way to use this Orbi mesh and keep AT&T.